The present invention relates to an image projection apparatus such as a liquid crystal projector, and more particularly to an image projection apparatus having a function of avoiding an overheated state inside of the apparatus.
In the image projection apparatus (hereinafter referred to as projector), while heat generating devices (exothermic devices) such as a light source and devices included in a power supply system are used, many heat-vulnerable components such as optical components and electrical elements which are formed of resin materials are used. Therefore, the projector has a heat exhausting structure (cooling structure) that cools the heat generating devices with airflows created by cooling fans and exhausts the airflows taking heat from the heat generating devices through an exhaust air outlet to the outside.
However, when the projector is used in a state in which the exhaust air outlet is disposed close to an obstacle such as an indoor wall (that is, in a state in which the exhaust air outlet is blocked), the heat exhaust efficiency of the projector is deteriorated, which causes an excessive temperature increase inside of the projector. Thereby, thermal damage occurs in the heat-vulnerable components, which may deteriorate the performance of the projector and reduce the lifetime thereof.
Japanese Patent Laid-Open No. 2001-312000 discloses a projector in which a temperature abnormality is determined when the temperature detected by a temperature sensor installed in the projector exceeds a predetermined temperature, and then a protection function is activated.
In addition, Japanese Patent No. 3895889 discloses a projector in which a temperature abnormality is determined when the increase rate of the temperature of the light source lamp exceeds a predetermined increase rate, and then a protection function is activated.
However, the projector is sometimes used such that, in a state in which the temperature around a temperature sensor placed, for example, in the vicinity of the light source lamp is still high due to residual heat of the lamp after being turned off, the lamp is re-lit. In such a case, in the projector disclosed in Patent Laid-Open No. 2001-312000, when the temperature around the temperature sensor at the time of re-lighting of the lamp exceeds a predetermined temperature that is a threshold temperature at which the protection function is activated, the protection function is mistakenly activated even though essentially there is no problem.
On the other hand, when compared to a case where the temperature increases due to the lighting of the lamp from a state in which the temperature around the temperature sensor is low, the increase rate of the temperature is lower in a case where the temperature further increases due to the re-lighting of the lamp from a state in which the temperature around the temperature sensor is high. Therefore, in the latter case, even if the projector disclosed in Japanese Patent No. 3895889 is used in the state in which the exhaust air outlet is blocked, the protection function may not be activated because the temperature increase rate detected by the temperature sensor does not exceed the predetermined increase rate.